| Author | Message | ||
     den Member Username: Den Post Number: 74 Registered: 03-2006 |
In a previous thread [http://www.dl-c.com/cgi-bin/discus/show.cgi?tpc=2&post=18283#POST18283], MarcelM, suggested an HSL curve solution for one of his images, IMG_0025, a rear view of the Paris Opera House and skyline. While the tone curve was not unusual, the saturation curve was. And my final preference image version resulting from a multi-step blended image approach has a heavy-handed gothic ambience. Others have variously suggested different gammas during/after RAW conversion and the Color Curves transform, most recently the Levels and Color transform. As an addition, here is a case for the Brightness Curve transform in the RGB color space. MarcelM’s IMG_0025, seems to be an ideal sample image as it has a two-peak histogram, i.e., there are two image areas that need separate treatment: the sky/clouds and the buildings. The optimizing curve for the buildings, which are of chief interest, will wash out the sky/cloud detail available if not masked. Workflow summary: A soft gradient transition mask separating the sky/clouds and buildings was formed using the Mask Tool – Brightness Curve in ‘Stair Step’ and ‘Log Histogram’ [or ‘High Resolution Histogram’ for PWP3.5/4.0] to locate the histogram dip between the sky/clouds and buildings; Add – Apply the determined ‘Stair Step’ curve; Apply Blur = 35; and then leave the mask active on the RAW converted working file. Click on the working file image and open the Brightness Curve transform and in the RGB color space form a curve and adjust mask white/black amounts to preference while monitoring the results in the Preview window. IMG_0025 specifics: ·Gamma: x-x ·Contrast: No expansion ·Color Profile: Canon Digital Rebel XT (0509wg22) ·Advanced settings ·Whitepoint: camera WP ·Color Space: sRGB ·Preferred Interpolation: AHD Gamma = 1.0  Gamma = 1.4  Gamma = 2.2  Summary/Conclusions/Comments [at least for this image]: 1. A single initial curve change in the RGB color space keeps the relationships between tone and color [saturation/hue] closer to the way they were recorded by the camera allowing simpler subsequent post-processing changes if needed/desired in PWP’s default HSV and/or the HSL color spaces and the Levels and Color or Color Curve transforms. 2. By changing the Brightness Curve histogram resolution to ‘Log Histogram’ or ‘High’, black/white points can be selected to keep the maximum available pixel data. When the Levels and Color transform’s ‘Full Range’ is used, slight clipping can occur with its black/white point selection when compared with the Brightness Curve and Color Curves transforms. 3. A Gamma >1.0 conversion does not compress the shadows/mid-tone tone range as much as Gamma = 1.0, making it easier to form the ‘Brightness’ curve and making it possible to form a brightening ‘S-Contrast’ curve. ‘S-Contrast’ or reversed ‘S-Contrast’ curve effects are not as easily achieved if the Levels and Color transform is used. If anyone has had a differing experience with their RAW conversion post-processing, I would like to know. I tried working with the Color Curves and Levels and Color transforms in HSV and HSL color spaces and could not achieve in only one transform operation and mask, images similar to the ones illustrated here with IMG_0025. Obviously, the image sampling is small and the generalizations may not hold. As time allows, I will document this approach for this image with higher resolution illustrations and curve and work-along files for your trials and closer inspection on my web sight in the near future. MarcelM… Thank you for making the IMG_0025 working images available to me. | ||
| den Member Username: Den Post Number: 76 Registered: 03-2006 |
Add'l Note: I was working from 799x1200 pixel, 100% jpg quality files of IMG_0025's full-sized RAW conversion to tiff working files. Please take this into account when you select the amount of transition mask blur to use when working with a full sized image [8 megapixel, for example]. If the blur is too small, halo will become too obvious. The Blur = 35 is for the 799x1200 sized image. Re-sizing and jpg compression required for illustration to the above post, emphasized the transition halo more than it shows on the monitor at full resolution. | ||
| den Member Username: Den Post Number: 80 Registered: 03-2006 |
A RGB curve was applied to IMG_0025_gamma_2-2.jpg that expanded the original buildings image area tone range of 7.5 -> 53% to 0 ->74.5% using a brightening 'S'-Contrast curve. The sky/cloud image area detail/contrast loss was limited to preference through a transition mask that identified the image's 53% tone value image areas [the lowest point between the two histogram peaks] with added Blur = 50 gradients. Workflow is detailed and a work-a-long image is linked here: A RGB Brightness Curve Approach 'Sun-Dappling' [a PWP3.1.h workflow carry over] is described/illustrated. This technique is used with either a hand painted mask or an image area mask generally combined in Overlap mode with a high contrast mask curve of the image area highlights and PWP's Filter transform The 'dappling mask' used with PWP3.5/4.x's Soft Light or Hard Light filters could also be used but would not add warm toning which may be desired to emphasize or create an early/late daylight ambience. The 'transition mask' acts as a virtual Neutral Density Filter where the Blur and the White/Black amounts simulate the differing filter densities. This masking technique has application to any two-peak histogram image where the tone range of one peak needs to be aggressively changed while minimizing changes to the other peak’s tone range…. And need not be limited to landscapes….  |
